Audio devices, including a conventional open fit hearing aid, are provided with a vent to let an inside of an external auditory canal communicate with the outside to reduce the sense of muffling when these devices are worn (Refer to Patent Literature 1, for example.) A conventional hearing aid includes a microphone, an earphone, and a vent. The microphone collects sound from a sound source, and the earphone enables a user to hear the sound collected by the microphone. The vent, as described above, is a hole that lets the inside of the external auditory canal communicate with the outside. The vent prevents occlusion of the external auditory canal, and accordingly, the user feels reduced sense of muffling when wearing the hearing aid.